1. Field of the Invention
The present invention relates to a total-bloodtype blood sugar analyzer for use in hospitals, clinics, and analyzer companies for analyzing the concentration of glucose or blood sugar in a blood specimen (total blood, blood serum, or blood plasma of a human being or animal) in a short period of time using a small amount of blood sample.
2. Description of the Prior Art
Blood sugar analyzers of the type described above measure a sugar content or glucose concentration by supplying a blood specimen or standard solution (hereinafter referred to as blood specimen or the like) with a blood sugar content to a fixed enzyme membrane (glucose oxidase membrane) to cause a chemical reaction therebetween, which generates a reaction current in proportion to the blood sugar contained in the blood. The blood sugar analyzers comprise a fixed enzyme membrane electrode (composed of an electrode surface of platinum and silver to which a membrane of blood sugar oxidase is intimately attached), and a reaction cell which houses the electrode and receives a blood specimen or the like. Since the chemical reaction is generally susceptible to temperatures, the blood sugar analyzers include a temperature sensor for detecting temperatures in the reaction cell to maintain the reaction cell and adjacent areas at a predetermined temperature under the control of an output from the temperature sensor.
FIG. 1 illustrates a conventional glucose analyzer, and FIG. 2 is a graph showing the output from a blood sugar sensor plotted against a measuring operation sequence of the analyzer.
An output from the blood sugar or glucose sensor in the analyzer is converted into a blood sugar or glucose concentration (in units of mg/dl) and displayed on a display 12. A conversion coefficient can be obtained by measuring a standard solution having a known blood sugar or glucose concentration which is introduced into an analyzer body 11 through an inlet port 14. It has been conventional practice in obtaining such a conversion coefficient to turn an adjustment knob 13 until a displayed value on the display 12 is brought into conformity with the known blood sugar concentration in the standard solution. However, such an adjustment is tedious and time-consuming, and a variable resistor actuatable by the knob 13 is required to be of a high precision, adding to the cost of the analyzer.
Obtaining a correct measurement requires that an offset portion (which corresponds to a base portion appearing as the output of the blood sugar sensor before a blood specimen or the like is introduced for measurement, and which is indicated by OFF in FIG. 2) be removed from the output of the blood sugar sensor. For such removal of the offset portion, it has been customary to establish a suitable threshold value TH in advance, to compare a sensor output SO with the threshold value TH, to regard a chemical reaction as being started when the sensor output SO becomes larger than the threshold value, and then to subtract the offset portion from the sensor output SO from that time on, thus reaching a net quantity involved in the reaction. However, the prior practice is disadvantageous in that, where the threshold value is too high, a blood sample with a low blood sugar concentration cannot be measured, and conversely, where the threshold value is too low, noises or variations in the base portion are included in measurements. The offset portion cannot correctly be defined for its value, and hence measurement results have not been accurate.
An enzyme membrane sensor used heretofore has suffered the drawback that it does not provide linearity in a range of higher concentrations, that is, the proportional relationship between measured values and actual concentrations is not assured in such a higher concentration range, resulting in a tendency to produce errors in measurement in a wide range of concentrations.
Also, the results of blood sugar concentration measurement have been handwritten, and hence wrong values are liable to be recorded in error.
The analyzer according to the prior art effects measurements by going through various modes of operation, as shown in FIG. 2, including introduction of a blood specimen or the like, allowing a chemical reaction to take place, washing away of the blood specimen or the like which has gone through the chemical reaction, and introduction of a next blood specimen or the like. The modes of operation are repeated for a number of measurements. Such modes of operation are divided by predetermined intervals of time, which are monitored to effect shifting from one mode to a next mode of operation. With such time-governed control, a transition may not be carried out even when the condition for such transition has already occurred, or a transition may be effected too early with the result that sufficient measurement may not be performed. Therefore, the analyzer has suffered a lowered capability of handling specimens or is prone to incorrect measurements. When the time interval for washing the reaction cell is too long, the analyzer has a lowered handling capability and is wasteful of a buffer liquid. Accordingly, a more efficient control system for controlling the time of washing would be desirable.